Interface for operating a dot matrix printer for printing a video image

Abstract

An electronic interface for operating a dot matrix printer to print a pattern appearing on a television screen employs video-type signals incorporating field and line sync signals, digitized image signals representative of dots of information along each raster line and dot pulses for synchronizing the digitized image signals. Upon receipt of a print request, a line address counter is incremented by each line sync pulse. A second counter, which is incremented each time the line address counter reaches a maximum count, has its count set into a horizontal position counter at the beginning of each line scan and is decremented synchronously with the dot pulses. The sequentially received dot information is loaded serially into a shift register and is transferred byte-wise in parallel into a location in a random access memory identified by the count in the line address counter when the horizontal position counter reaches a zero count. When the line address counter reaches its maximum count, the interface circuitry prints the stored bytes, representing a "slice" of the raster image in an orientation transverse to the direction of the lines comprising the raster image. Successive "slices" are acquired and printed in a similar fashion to collectively create a completed image.

What is claimed is: 
     
       1. A method for storing data for use in operating a printer of the dot matrix type from digitized video data comprising a composite sync signal incorporating field and line sync signals, a data signal incorporating digitized image data, and a clock signal incorporating regularly occurring time pulses for use in synchronizing the digitized data signals, said method comprising the steps of: initiating an acquired data cycle upon detection of a next field signal when the printer is ready to print;   counting line sync signals occurring after the detection of the last-mentioned field sync signal;   counting timing pulses occurring after detection of each line sync signal; and   selecting a predetermined portion, less than the whole of the image data of each line, in accordance with the timing pulse count, for storage in a random access memory at locations in the memory determined in accordance with the line count associated with the portion of image data being stored.   
     
     
       2. A method for operating the print head of a printer to print a dot pattern upon a print receiving medium from lines of digitized image data which comprise a composite image, said method comprising the steps of storing a portion of said image in a memory having a plurality of memory locations, each location storing a line portion of and less than one line of digitized image data, said line portions representing a plurality of dot signals,   utilizing a composite signal containing field and line sync signals and a timing signal incorporating timing pulses for use in synchronizing said digitized image data,   said method further comprising the steps of:   initiating a print cycle when the print head is in position to print;   repeatedly incrementing a line count;   reading out the contents of the memory location associated with said line count each time said line count is incremented;   operating the associated dot generating means of the printer to print in accordance with the dot representing signals stored in each read memory location; and   moving the print head across the print receiving medium after each print step.   
     
     
       3. The method of claim 2 further comprising returning the printing element to a starting position preparatory to printing the next line of dot patterns; storing image data for printing the next line of dot patterns in said memory.   
     
     
       4. The method of claim 2 wherein the image data stored in memory is printed by moving the printing element in a direction transverse to the lines of image data. 
     
     
       5. The method of claim 2 further comprising the steps of detecting the presence of each print position and generating a registration pulse for each print position;   counting the registration pulses;   successively reading out the contents of each memory location associated with each count; and   operating the printing element to print a dot pattern in accordance with the image data read out of the memory location.   
     
     
       6. Apparatus for operating a dot matrix printer from a composite video-type signal comprising signals representing image information for each line of a raster image and field and line sync signals, said apparatus comprising: means for detecting said field sync signals;   first digital counter means for counting line sync signals after the occurrence of a said field sync signal;   memory means having address inputs cooled to said first counter means for selecting a memory location in accordance with the count in said first counter means;   conversion means for converting said image information signals into sequential digital signals;   said memory means including data inputs coupled to the outputs of said conversion means for writing digital signals from said conversion means into a memory location selected in accordance with said first counting means; and   second counting and control means for selecting a portion, less than a whole line, of the information of each line of the raster image to transfer into the memory means from said conversion means.   
     
     
       7. The apparatus of claim 6 further comprising means responsive to said first counter means reaching a predetermined count to terminate the loading of digital signals into said memory means and for initiating a print cycle. 
     
     
       8. The apparatus of claim 7 further comprising a print head means;   means for moving said print head means responsive to initiation of a print cycle;   means responsive to movement of said print head means for generating registration pulses;   means responsive to said registration pulses and initiation of said print cycle for causing said first counter means to count in a reverse direction;   means responsive to initialization of said print cycle for placing said memory means in a read mode; and   means for coupling each digital signal stored in said memory to said print head means for operating said print head means to print a dot pattern from a said memory location selected in accordance with the count in said first counter means.   
     
     
       9. The apparatus of claim 8 further comprising means responsive to said first counter means reaching a second predetermined count for terminating a said print cycle and initiating a subsequent data acquisition cycle. 
     
     
       10. The apparatus of claim 8 wherein said registration pulses are adapted to decrement the count of said first counter means. 
     
     
       11. The apparatus of claim 6 further comprising third counter means;   means responsive to each field sync signal for advancing the count of said third counter means; and   means responsive to each line sync signal for loading the contents of said third counter means into said second counter means.   
     
     
       12. The apparatus of claim 11 wherein said second counter means further comprises means responsive to said image data for decrementing said second counter means; and   means responsive to said second counter means reaching a predetermined count for preventing the transfer of further image data to said conversion means.   
     
     
       13. The apparatus of claim 11 further comprising settable means for selectively setting a predetermined count in said third counter means. 
     
     
       14. The apparatus of claim 11 further comprising means responsive to the count in said third counter means for terminating a printing operation. 
     
     
       15. The apparatus of claim 11 further comprising extraction means for extracting the field sync signals from said composite signal for application to said third counter means. 
     
     
       16. The apparatus of claim 6 further comprising means responsive to said first counter means reaching a predetermined count for resetting said first counter means to thereby prevent a predetermined number of lines from being printed. 
     
     
       17. The apparatus of claim 6 further comprising switch means for initiating a printing operation; means responsive to operation of said switch means for initiating a printing cycle.   
     
     
       18. The apparatus of claim 6 further comprising input means for receiving said TV-type signals, cable means for coupling the TV-type signals to said input means; said input means comprising means for matching the impedance of the incoming cable coupled to said input means and digitizing means for digitizing the signals coupled thereto. 
     
     
       19. The apparatus of claim 18 wherein said digitizing means comprises differential amplifier means. 
     
     
       20. The apparatus of claim 19 further comprising means for applying a threshold level to one input of said differential amplifier means, said cable being coupled to a second input of said differential amplifier means. 
     
     
       21. The apparatus of claim 6 further comprising extraction means for receiving said composite signal and for extracting the line sync signals for application to said first counter means. 
     
     
       22. The apparatus of claim 6 wherein said conversion means comprises multi-stage shift register means having an input for receiving image data and having outputs coupled to the data inputs of said memory means. 
     
     
       23. The apparatus of claim 6 wherein said line sync signals are adapted to increment the count of said first counter means.